Types of Volcano, What is Volcano, What is Vulcanicity, Components of Volcano,Types of Lavas, Effect of Volcanic Eruptions
What is Volcano
The word volcano is derived from the name of ‘Vulcano’, a volcanic island in the Aeolian Islands of Italy whose name in turn originates from ‘Vulcan’, the name of god of fire in Roman mythology. ‘Volcanology’ or ‘Vulcanology’ is the term given to the study of volcanoes, and scientists who study them are called the ‘Volcanologists’ or ‘Vulcanologists’.
Volcano is a vent or an opening through which heated materials consisting of water, gases, liquid, lava and rock fragments are erupted from the highly heated interior to the surface of the earth. The layer below the solid crust of earth is mantle. It has higher density than that of the crust. The mantle contains a weaker zone called asthenosphere. It is from this that the molten rock materials find their way to the surface. The material in the upper mantle portion is called magma. Once it starts moving towards the crust or it reaches the surface, it is referred to as lava.
What is Vulcanicity
Vulcanicity includes all those process in which molten rock material or magma rises to the crust to solidify as crystalline or semi-crystalline rocks. Some scientists use vulcanism as a synonym for vulcanicity.
Vulcanicity has to components; one of them operates below the crustal surface and other above the crust that is the endogenetic mechanism and exogenous mechanism. The endogenetic mechanism includes the creation of hot and liquid magma and gases in the mantle and the crust, their expansion and upward ascent, their intrusion and cooling and solidification in various forms below the crustal surface. The exogenous mechanism includes the process of the appearance of lava, volcanic dust and ashes, fragmental materials, mud, smoke etc, in different forms on the earth’s surface.
Causes of Vulcanism
The mechanism of vulcanism and the volcanic activity are associated with several processes, such as:
– A gradual increase of temperature with increasing depth at the rate of 1 degree Celsius for every 32 m.
– Magma is formed due to the lowering of melting point, which in turn is caused by the reduction in pressure of the overlying material.
– Gases and vapour are formed due to heating of water, which reaches underground through percolation.
– The ascent of magma host by first volume of gases and water vapour.
– The occurrence of volcanic eruption.
Components of a Volcano
The volcanoes of explosive type have a volcanic cone, which is form when the erupt material accumulates around the vent. The vent is an opening of circular or nearly circular shape at the centre of the cone. The vent is connect to the interior of the earth by a narrow pipe. The volcanic materials erupt prove this pipe. If funnel shaped hollow at the top of the cone is called the crater.
Types of Lavas
1. Basic Lavas
These are the hottest lavas and are highly fluid. They are dark colour like basalt, rich in Iron and magnesium but poor in silica. They flow quietly and are not very explosive. The affected expensive areas, spreading out as thin sheets over great distances before they solidify. The resultant volcano is gently sloping with a white diameter and forms a flattened shield or dome.
2. Acid Lavas
These lavas are highly viscous with a high melting point. They are light in colour, of low density and have a high percentage of silica. They flow slowly and seldom travel far before solidifying. The resultant volcano is there for a steep-sided. The rapid cooling of lava in the vent obstructs the flow of the outpouring lava, resulting in loud explosions throwing out many volcanic bombs or pyroclasts. Pyroclasts are any volcanic fragment that was hurled through the air by volcanic activity.
Types of Volcanoes
There is a wide variation in the mode of volcanic eruption and their periodicity. Accordingly, the volcanoes can be classified on the basis of the mode of eruption and their periodicity of eruption.
Classification on the basis of mode of eruption
1. Violent or Explosive Type
The eruption of violent or explosive type is so rapid that huge quantities of volcanic materials ejects thousands of metres in the sky. On falling, these materials accumulate around the volcanic vent and form volcanic cones. Such volcanoes are very destructive. They are generally link with acidic lavas.
2. Effusive or Fissure Type
The eruption of the fissure type of volcanoes-occurs along a long fracture, fault or fissure. Magma ejects slowly and the resultant lava spreads on the surface. The speed of the lava flow depends on the nature and volume of magma, slope of the ground and the temperature conditions.
Classification on the basis of periodicity of eruption
1. Active Volcanoes
Active Volcanoes which frequently erupt or at least when they have erupt within recent time. Etna and Stromboli a typical example.
2. Dormant Volcanoes
Volcanoes known to erupt and show signs of possible eruption in future are describe as dormant. Mt. Vesuvius is the best example.
3. Extinct Volcanoes
Volcanoes that have not erupted at all in historic times but a retain the feature of volcanoes are termed extinct. Ship rock in Netherland is one such example. All volcanoes pass through active, dormant and extinct stages but it is impossible to be thoroughly sure when a volcano has become extinct.
Effects of Volcanic Eruptions
1. Large volume so hot lava moving at a first speed can bury man made buildings. It can also kill people and animals, destroy agriculture farms and pastures, burn and destroy forests.
2. The fall out of large quantities of fragmented materials, dust, ash, smoke etc., Create health hazards due to poisonous gases emitted during eruption. It also cause acid rain.
3. If the explosive eruption has occur suddenly, the human beings get no time to escape to safer places. Heavy rains mixed with volcanic dust and ash cause enormous mud flow on the steep slopes of the cones.
4. Earthquakes caused due to explosive eruptions can generate destructive tsunamis, seismic waves etc. These can cause loss of life and property in the affected coastal regions.
5. The volcanic eruptions can change the heat balance of the Earth and the atmosphere causing climate changes.
1. Lava can give rise to fertile soils. Most of the precious stones form due to volcanic activity.
2. Geysers and springs are tourist attraction and are also important from the medical point of view due to the chemicals dissolved in them.
3. Some crator lakes are source of rivers and often offer scenic attraction of tourists.
4. Most of the volcanic rocks when exposed on the surface are a storehouse of metals and minerals.